Apparatus for maintaining uniform resistance in electric circuits.



' 'No. 727,611. 1 PATENTED MAY 12, 1903.

E. A. GILBERT E. 0. LUNDINZ APPARATUS FOR MAINTAINING UNIFORM RESISTANCE IN ELEGFIRIG CIRCUITS. on 1! mam-1am.

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UNITED STATES Patented May 12. 1903.

PATENT OFFICE.

FREDERICK A. GILBERT, OF BROOKLINE, AND EHIL'O. LUNDmorBEAon MONT, MASSACHUSETTS, ASSIGNORS TO THE GENERAL ELECTRIC ooM- PANY, A CORPORATION OF NEW YORK.-

APPARATUS FORMAINTAINING UNIFORM RESISTANCE mercuric tiiicuns.

SPECIFICATION forming part of Letters Patent No. 727,611, dated M y 12, 1903; i Application 51st November 22,1897. seen to. 659,391, (No modehl IO specification, like characters on the drawings representing like parts.

In electrical apparatus it is often very desirable to maintain a substantially uniform resistance in a circuit which, owing to some extraneous cause or causes, is liable to have its resistance changed or varied-that is to say, it a resistance medium having a certain resistance under normal conditions is. included'in a circuit some extraneous causo so as, for instance, a change in temperature+ will so vary that resistance that it will be greater or lessthan the normal resistance. Now in such case the resistance of thecircuit may be maintained substantially normal if the effective extentof such resistanceinedium is varied inversely to and to compensate for the change efi'ected in the specific resistance of such medium, so that if the resistance be increased the etfective extent of the medium o will be decreased, and vice versa. One common instance of the variation in resistance in a circuit by extraneous causation is in the electric-arc lamp. When the current 'is turned on, the carbons will be separated to form the arc, and the feed-controlling circuit has a certain resistance. After the lamp has burned for some time the resistance of the feed-controlling circuit will increase by the rise in temperature of the lamp and a change 40 in the sensitiveness of feed results. Besides this, heatingof thelamp orit-s circuits changes the point at which feed is efiec'tid. In order to obviate this objectionable feature, the present practice is to make the normal resistance 5 of the feed-controlling circuit less than that required to attain the proper length of are, so that therproper resistance will not be reached until. the lamp has become heated. As a re- A sult the arc is too short during the time the lamp is heating,with a correspondingly poor light. In our-experiments to improve the service of electric-arc lamps, so that the light will be good when the lamp is started,We'ha-ve discovered that the resistanceof a circuit may be maintained substantially uniform by varying the eltective extent of the resistance medium included in such circuit inversely to and to compensate for the change'in thespecific resistance of such medium due to an extraneous cause.

In our present invention We have made a practical embodiment of our discovery in an electric-arc lamp, and we are enabled thereby to employ the proper resistanc'e'at the start, so that the proper separation of the carbons is attained. at once.

When theresistance'increases by reason of the heating of the lamp, the effective extent of the resistance medium is reduced, so that the arc is shortened and the normal or proper resistance is again attained under such changed conditions and retained while the lamp is burning. After the arc has been so shortened the subsequent regulation thereof is effected in the usual manner.

Figure l, in elevation, represents a sufficient portion of an arc-lamp frame to be understood with one embodiment of our invention applied thereto. Fig. 2 is a top or plan view of the apparatus shown in Fig. 1,-and Fig. 3 is a diagrammatical representation of the circuits through the thermostat and arc-lamp.

Referring to Fig. 1, a metal bo'd'y portion A (see dotted lines) is provided with abase A and top A the upper carbon passing through the body, top, and base, substam tially as shown in United States patent granted to us, No. 603,630, of May 10,1898. In our present invention, however, we, have shownthe series coil 0 as wound upon a'suit- 1 able core at the upper portion of the lampbody, the coil being included between the top A and a plate A of insulating materiallocated about midway between the top and base, the current acting through the series coil to raise the upper carbon by any usual or desired mechanism. The current enters nected 'with the m etal body, and passes thence to the upper carbon by suitable contacts, then from the lower carbon by wired) to one end of the series coil C, through the latter, and back 'to line at L. The shunt-coil is located between the base A and the partitiou A and while it is practically -a"s'ingle coil it is preferably made in two parts R and R, the former of copper wire and the latter of German-silver wire, as the resistance of the latter is so much greater than copper wire that' a very much smaller quantity of it is required, the part R being cut out: or shortcircuited under ordinary circumstances after the lamp has been burning for some time, as willbe described. The coil as a whole is in shunt with the are, one end being connected at 'r with the lamp-body and theother end with "the line-wire L by wire 7*. The adjacent ends of'th'e two coils are connected bya wire rwith a metal terminal support 1), insulated; from and mounted upon a metallic ring B, secured to standards 35 on the t'op A of the body. One end of athermostat- 'l is attached by suitable screws t to the ring B, its free end passing through a guide tand preferably being bent over, as' at t", to form a movable terminal adapted'to cooperate with an adjustable fixed terminal 1), (shown as a screw mounted in the support 1),) which permits a predetermination of the point at which the lamp shall feed when hot. When the lamp'is cold, the thermostat contract-s, separating the terminals b If, so that the entire resistance due to both coils will be'effective when the lamp-current is turned on, and consequently the current passing through the shunt-coil R R will be decreased, so that the current passing through the series coil '0 will lift the upper carbon with a strong pull and form the arc.

The total resistance of the coils R R is such thatwhen the lamp'is started the fpll separations of the carbons is permitted; but after the lamp has been burning long enough to necessitate feed of the carbon to compensate for th burning away thereof the heating of the lamp will have acted to raise the resist ance in the coils R R, so that suflicient current-cannot pass through the shunt-coil to draw the carbons together and the arc will be too long. By our invention, however, we are enabled to automatically reduce the resistance so that the proper length of are can be attained.

As the lamp heats, the rise in temperature acts upon the thermostat T, expanding it so that the terminals t and b are broughttogether, and the part- R of the shunt-coil is short-circuited or cut out, so that only the burning. great number of lamps are in sheltered 10- resistance of the coil R is effective. This reduction of the resistance in the shunt-circuitpermitsmorecurrenttepasstherethrough and the upper carbon is; drawn down to shorten the arc to the proper length, and after such actionthe resistance will be suflicient to properly control the feed of the carbon.

It will be obvious that if the lamp is in an exposedposition during cold weather the re.- sistance ofthe shunt-coil will not be materially increased, because the su rroundin'gcold air will obviate heating when the lamp is As a matter of fact, however, a

calities ornin buildings, and whenever the heating of the lamp is snflicient to unduly increase the resistance our invention is extremely valuable in increasing the effectiveness of the lamp.

embodiment of our invention, the same may be modified or altered in various particulars without departing from the spirit and scope of our invention. 1

Having fully described our invention, what we claim, and desire to'secure by Letters Pat.- ent, is-- H 1'. Means forcompensating change of resistance of an'electric circnitdue to heating,

comprising 'a normally open short circuit around a part of the circuit, an adjustable thermostat for predetermining the pointof action, and a circuit-controller operated thereby at a definite temperature for which the device is set to close the short circuit.

2; Thecombination, with an arc-lamp, of an adjustable thermostat, a short circuit for part o'fthelamp-shnnt, and means controlled r While we have herein shown one practical iOf,

shunt-coil, composed of two conductors of different specific resistance, and means forcutting out one coil at a determinate temperature.

4. An arc-lamp having a series coil, a shunt-coil having two sections, one of German silver, and the other of copper, and a cut-out for the German-silver coii acting at adeterminate temperature.

In testimony whereof we have signed our names to this specification in the presence of two subscribing witnesses.

FREDERICK A. GILBERT. EMIL O. LUNDIN.

Witnesses:

SAMUEL S. SIAS, CHARLES A. SNOW. 

